Effects of spray application of urea fertilizer at stem extension on winter wheat: N recovery and nitrate leaching

Abstract

A field experiment was carried out at Harper Adams in Shropshire to investigate the effect of supplying the spring N application to winter wheat as different proportions of urea as a solution, rather than as conventional soil-applied solid urea, on N recovery in the above-ground crop, autumn soil mineral N and nitrate leaching over the subsequent winter. A solid ammonium nitrate treatment was also included to represent alternative commercial practice to solid urea. Treatments were repeated on the same plots over the 3 years 1992, 1993 and 1994. N recovery was measured in all 3 years by difference in N uptake between fertilized and unfertilized plots, and in 1993 for selected treatments, N was applied as "&N-labelled fertilizer to determine direct uptake of fertilizer N in the crop and soil. Both urea sprays and solid soil N applications were labelled with "&N. Urea sprays were split over several days to reduce scorch, whereas solid fertilizer was applied as a single dressing. For some urea spray treatments, apparent N recovery in the above-ground crop in 1992 and 1994 was less compared with soil-applied N treatments. These urea spray treatments were applied in the morning rather than the evening, and gaseous losses, most likely by volatilization, are suggested. In 1992 application of a large proportion of N as urea sprays, such that application of some N as urea solution was delayed to around GS 37, was associated with an increase in physiological N use efficiency. In 1993, there was no difference in direct or apparent recovery of fertilizer N in the crop or soil for N applied as ammonium nitrate, solid urea or as urea sprays. Mean nitrate concentration in the drainage water at 1 m was elevated for all N treatments in all years, but only in 1992 did nitrate concentration and leaching loss decrease with increasing proportion of N applied as urea sprays. It may therefore be possible to reduce gaseous losses by application of urea sprays under cool conditions in the evening and exploit the increased physiological N use efficiency for urea sprays applied later, such that total fertilizer N applied and N losses are reduced.

The effect of different forms of nitrogen fertilizers on nitrogen leaching

“…As a result, nitrogen fertilizers of different chemical composition may have various effects on nitrogen leaching and environmental pollution. Experiments performed in England showed that under different climatic conditions nitrogen uptake and leaching from liquid and granular urea and ammonium nitrate varied (Readman et al, 2002). In one year, plants assimilated more nitrogen from liquid fertilizer, the next year no differences were observed.…”

Planting Date and Nitrogen Effects on Grain Yield and Protein Content of Spring Wheat

“…Smith et al (1991) observed positive increases in GPC with foliar N application, and greater increase in GPC was obtained when the application was made close to flowering. However, Readman et al (2002) reported no additional yield advantage of foliar‐sprayed urea as compared to the soil applied fertilizer. Woolfolk et al (2002) concluded that late season foliar N applications before or immediately after flowering may significantly enhance GPC in winter wheat.…”

“…The recovery of foliar‐applied N at the later stages of wheat development has been assessed using Isotopic 15 N labeling (Powlson et al, 1989; Smith et al, 1991; Rawluk et al, 2000; Readman et al, 2002). Powlson et al (1989) at Rothamsted, UK reported a recovery of about 70% of the foliar‐applied N given at anthesis in the aboveground parts, including 64% in grains.…”

Effect of in-season application methods of fertilizer nitrogen on grain yield and nitrogen use efficiency in maize

“…Using a 15 N-labeling technique can help determine the recovery of foliar-applied N in wheat (Triticum aestivum L.) (Powlson et al 1989;Smith et al 1991;Rawluk et al 2002). Powlson et al (1989) reported that the recovery could be up to 70% through foliar application of N at anthesis in the aboveground parts including 64% in grains, whereas Rawluk et al (2000) recently reported that the recovery of foliar-applied N in wheat grain was much lower (5.5 to 26.7%) than that of soil-applied N (32.3 to 70.1%), and grain yield and protein were also higher for soil-applied than for foliar-applied N. Similarly, Readman et al (2002) observed a lower recovery of foliar-applied N than in the soil-applied treatment. Smith et al (1991) observed that grain N concentration increased with foliar N application and a greater increase in grain protein occurred when the application was close to flowering.…”